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 // SPDX-License-Identifier: GPL-2.0
 #include <linux/ceph/ceph_debug.h>
 
 #include <linux/sort.h>
 #include <linux/slab.h>
 #include <linux/iversion.h>
 #include "super.h"
 #include "mds_client.h"
 #include <linux/ceph/decode.h>
 
 /* unused map expires after 5 minutes */
 #define CEPH_SNAPID_MAP_TIMEOUT (5 * 60 * HZ)
 
 /*
  * Snapshots in ceph are driven in large part by cooperation from the
  * client.  In contrast to local file systems or file servers that
  * implement snapshots at a single point in the system, ceph's
  * distributed access to storage requires clients to help decide
  * whether a write logically occurs before or after a recently created
  * snapshot.
  *
  * This provides a perfect instantanous client-wide snapshot.  Between
  * clients, however, snapshots may appear to be applied at slightly
  * different points in time, depending on delays in delivering the
  * snapshot notification.
  *
  * Snapshots are _not_ file system-wide.  Instead, each snapshot
  * applies to the subdirectory nested beneath some directory.  This
  * effectively divides the hierarchy into multiple "realms," where all
  * of the files contained by each realm share the same set of
  * snapshots.  An individual realm's snap set contains snapshots
  * explicitly created on that realm, as well as any snaps in its
  * parent's snap set _after_ the point at which the parent became it's
  * parent (due to, say, a rename).  Similarly, snaps from prior parents
  * during the time intervals during which they were the parent are included.
  *
  * The client is spared most of this detail, fortunately... it must only
  * maintains a hierarchy of realms reflecting the current parent/child
  * realm relationship, and for each realm has an explicit list of snaps
  * inherited from prior parents.
  *
  * A snap_realm struct is maintained for realms containing every inode
  * with an open cap in the system.  (The needed snap realm information is
  * provided by the MDS whenever a cap is issued, i.e., on open.)  A 'seq'
  * version number is used to ensure that as realm parameters change (new
  * snapshot, new parent, etc.) the client's realm hierarchy is updated.
  *
  * The realm hierarchy drives the generation of a 'snap context' for each
  * realm, which simply lists the resulting set of snaps for the realm.  This
  * is attached to any writes sent to OSDs.
  */
 /*
  * Unfortunately error handling is a bit mixed here.  If we get a snap
  * update, but don't have enough memory to update our realm hierarchy,
  * it's not clear what we can do about it (besides complaining to the
  * console).
  */
 
 
 /*
  * increase ref count for the realm
  *
  * caller must hold snap_rwsem.
  */
 void ceph_get_snap_realm(struct ceph_mds_client *mdsc,
              struct ceph_snap_realm *realm)
 {
     lockdep_assert_held(&mdsc->snap_rwsem);
 
     /*
      * The 0->1 and 1->0 transitions must take the snap_empty_lock
      * atomically with the refcount change. Go ahead and bump the
      * nref here, unless it's 0, in which case we take the spinlock
      * and then do the increment and remove it from the list.
      */
     if (atomic_inc_not_zero(&realm->nref))
         return;
 
     spin_lock(&mdsc->snap_empty_lock);
     if (atomic_inc_return(&realm->nref) == 1)
         list_del_init(&realm->empty_item);
     spin_unlock(&mdsc->snap_empty_lock);
 }
 
 static void __insert_snap_realm(struct rb_root *root,
                 struct ceph_snap_realm *new)
 {
     struct rb_node **p = &root->rb_node;
     struct rb_node *parent = NULL;
     struct ceph_snap_realm *r = NULL;
 
     while (*p) {
         parent = *p;
         r = rb_entry(parent, struct ceph_snap_realm, node);
         if (new->ino < r->ino)
             p = &(*p)->rb_left;
         else if (new->ino > r->ino)
             p = &(*p)->rb_right;
         else
             BUG();
     }
 
     rb_link_node(&new->node, parent, p);
     rb_insert_color(&new->node, root);
 }
 
 /*
  * create and get the realm rooted at @ino and bump its ref count.
  *
  * caller must hold snap_rwsem for write.
  */
 static struct ceph_snap_realm *ceph_create_snap_realm(
     struct ceph_mds_client *mdsc,
     u64 ino)
 {
     struct ceph_snap_realm *realm;
 
     lockdep_assert_held_write(&mdsc->snap_rwsem);
 
     realm = kzalloc(sizeof(*realm), GFP_NOFS);
     if (!realm)
         return ERR_PTR(-ENOMEM);
 
     /* Do not release the global dummy snaprealm until unmouting */
     if (ino == CEPH_INO_GLOBAL_SNAPREALM)
         atomic_set(&realm->nref, 2);
     else
         atomic_set(&realm->nref, 1);
     realm->ino = ino;
     INIT_LIST_HEAD(&realm->children);
     INIT_LIST_HEAD(&realm->child_item);
     INIT_LIST_HEAD(&realm->empty_item);
     INIT_LIST_HEAD(&realm->dirty_item);
     INIT_LIST_HEAD(&realm->rebuild_item);
     INIT_LIST_HEAD(&realm->inodes_with_caps);
     spin_lock_init(&realm->inodes_with_caps_lock);
     __insert_snap_realm(&mdsc->snap_realms, realm);
     mdsc->num_snap_realms++;
 
     dout("%s %llx %p\n", __func__, realm->ino, realm);
     return realm;
 }
 
 /*
  * lookup the realm rooted at @ino.
  *
  * caller must hold snap_rwsem.
  */
 static struct ceph_snap_realm *__lookup_snap_realm(struct ceph_mds_client *mdsc,
                            u64 ino)
 {
     struct rb_node *n = mdsc->snap_realms.rb_node;
     struct ceph_snap_realm *r;
 
     lockdep_assert_held(&mdsc->snap_rwsem);
 
     while (n) {
         r = rb_entry(n, struct ceph_snap_realm, node);
         if (ino < r->ino)
             n = n->rb_left;
         else if (ino > r->ino)
             n = n->rb_right;
         else {
             dout("%s %llx %p\n", __func__, r->ino, r);
             return r;
         }
     }
     return NULL;
 }
 
 struct ceph_snap_realm *ceph_lookup_snap_realm(struct ceph_mds_client *mdsc,
                            u64 ino)
 {
     struct ceph_snap_realm *r;
     r = __lookup_snap_realm(mdsc, ino);
     if (r)
         ceph_get_snap_realm(mdsc, r);
     return r;
 }
 
 static void __put_snap_realm(struct ceph_mds_client *mdsc,
                  struct ceph_snap_realm *realm);
 
 /*
  * called with snap_rwsem (write)
  */
 static void __destroy_snap_realm(struct ceph_mds_client *mdsc,
                  struct ceph_snap_realm *realm)
 {
     lockdep_assert_held_write(&mdsc->snap_rwsem);
 
     dout("%s %p %llx\n", __func__, realm, realm->ino);
 
     rb_erase(&realm->node, &mdsc->snap_realms);
     mdsc->num_snap_realms--;
 
     if (realm->parent) {
         list_del_init(&realm->child_item);
         __put_snap_realm(mdsc, realm->parent);
     }
 
     kfree(realm->prior_parent_snaps);
     kfree(realm->snaps);
     ceph_put_snap_context(realm->cached_context);
     kfree(realm);
 }
 
 /*
  * caller holds snap_rwsem (write)
  */
 static void __put_snap_realm(struct ceph_mds_client *mdsc,
                  struct ceph_snap_realm *realm)
 {
     lockdep_assert_held_write(&mdsc->snap_rwsem);
 
     /*
      * We do not require the snap_empty_lock here, as any caller that
      * increments the value must hold the snap_rwsem.
      */
     if (atomic_dec_and_test(&realm->nref))
         __destroy_snap_realm(mdsc, realm);
 }
 
 /*
  * See comments in ceph_get_snap_realm. Caller needn't hold any locks.
  */
 void ceph_put_snap_realm(struct ceph_mds_client *mdsc,
              struct ceph_snap_realm *realm)
 {
     if (!atomic_dec_and_lock(&realm->nref, &mdsc->snap_empty_lock))
         return;
 
     if (down_write_trylock(&mdsc->snap_rwsem)) {
         spin_unlock(&mdsc->snap_empty_lock);
         __destroy_snap_realm(mdsc, realm);
         up_write(&mdsc->snap_rwsem);
     } else {
         list_add(&realm->empty_item, &mdsc->snap_empty);
         spin_unlock(&mdsc->snap_empty_lock);
     }
 }
 
 /*
  * Clean up any realms whose ref counts have dropped to zero.  Note
  * that this does not include realms who were created but not yet
  * used.
  *
  * Called under snap_rwsem (write)
  */
 static void __cleanup_empty_realms(struct ceph_mds_client *mdsc)
 {
     struct ceph_snap_realm *realm;
 
     lockdep_assert_held_write(&mdsc->snap_rwsem);
 
     spin_lock(&mdsc->snap_empty_lock);
     while (!list_empty(&mdsc->snap_empty)) {
         realm = list_first_entry(&mdsc->snap_empty,
                    struct ceph_snap_realm, empty_item);
         list_del(&realm->empty_item);
         spin_unlock(&mdsc->snap_empty_lock);
         __destroy_snap_realm(mdsc, realm);
         spin_lock(&mdsc->snap_empty_lock);
     }
     spin_unlock(&mdsc->snap_empty_lock);
 }
 
 void ceph_cleanup_global_and_empty_realms(struct ceph_mds_client *mdsc)
 {
     struct ceph_snap_realm *global_realm;
 
     down_write(&mdsc->snap_rwsem);
     global_realm = __lookup_snap_realm(mdsc, CEPH_INO_GLOBAL_SNAPREALM);
     if (global_realm)
         ceph_put_snap_realm(mdsc, global_realm);
     __cleanup_empty_realms(mdsc);
     up_write(&mdsc->snap_rwsem);
 }
 
 /*
  * adjust the parent realm of a given @realm.  adjust child list, and parent
  * pointers, and ref counts appropriately.
  *
  * return true if parent was changed, 0 if unchanged, <0 on error.
  *
  * caller must hold snap_rwsem for write.
  */
 static int adjust_snap_realm_parent(struct ceph_mds_client *mdsc,
                     struct ceph_snap_realm *realm,
                     u64 parentino)
 {
     struct ceph_snap_realm *parent;
 
     lockdep_assert_held_write(&mdsc->snap_rwsem);
 
     if (realm->parent_ino == parentino)
         return 0;
 
     parent = ceph_lookup_snap_realm(mdsc, parentino);
     if (!parent) {
         parent = ceph_create_snap_realm(mdsc, parentino);
         if (IS_ERR(parent))
             return PTR_ERR(parent);
     }
     dout("%s %llx %p: %llx %p -> %llx %p\n", __func__, realm->ino,
          realm, realm->parent_ino, realm->parent, parentino, parent);
     if (realm->parent) {
         list_del_init(&realm->child_item);
         ceph_put_snap_realm(mdsc, realm->parent);
     }
     realm->parent_ino = parentino;
     realm->parent = parent;
     list_add(&realm->child_item, &parent->children);
     return 1;
 }
 
 
 static int cmpu64_rev(const void *a, const void *b)
 {
     if (*(u64 *)a < *(u64 *)b)
         return 1;
     if (*(u64 *)a > *(u64 *)b)
         return -1;
     return 0;
 }
 
 
 /*
  * build the snap context for a given realm.
  */
 static int build_snap_context(struct ceph_snap_realm *realm,
                   struct list_head *realm_queue,
                   struct list_head *dirty_realms)
 {
     struct ceph_snap_realm *parent = realm->parent;
     struct ceph_snap_context *snapc;
     int err = 0;
     u32 num = realm->num_prior_parent_snaps + realm->num_snaps;
 
     /*
      * build parent context, if it hasn't been built.
      * conservatively estimate that all parent snaps might be
      * included by us.
      */
     if (parent) {
         if (!parent->cached_context) {
             /* add to the queue head */
             list_add(&parent->rebuild_item, realm_queue);
             return 1;
         }
         num += parent->cached_context->num_snaps;
     }
 
     /* do i actually need to update?  not if my context seq
        matches realm seq, and my parents' does to.  (this works
        because we rebuild_snap_realms() works _downward_ in
        hierarchy after each update.) */
     if (realm->cached_context &&
         realm->cached_context->seq == realm->seq &&
         (!parent ||
          realm->cached_context->seq >= parent->cached_context->seq)) {
         dout("%s %llx %p: %p seq %lld (%u snaps) (unchanged)\n",
              __func__, realm->ino, realm, realm->cached_context,
              realm->cached_context->seq,
              (unsigned int)realm->cached_context->num_snaps);
         return 0;
     }
 
     /* alloc new snap context */
     err = -ENOMEM;
     if (num > (SIZE_MAX - sizeof(*snapc)) / sizeof(u64))
         goto fail;
     snapc = ceph_create_snap_context(num, GFP_NOFS);
     if (!snapc)
         goto fail;
 
     /* build (reverse sorted) snap vector */
     num = 0;
     snapc->seq = realm->seq;
     if (parent) {
         u32 i;
 
         /* include any of parent's snaps occurring _after_ my
            parent became my parent */
         for (i = 0; i < parent->cached_context->num_snaps; i++)
             if (parent->cached_context->snaps[i] >=
                 realm->parent_since)
                 snapc->snaps[num++] =
                     parent->cached_context->snaps[i];
         if (parent->cached_context->seq > snapc->seq)
             snapc->seq = parent->cached_context->seq;
     }
     memcpy(snapc->snaps + num, realm->snaps,
            sizeof(u64)*realm->num_snaps);
     num += realm->num_snaps;
     memcpy(snapc->snaps + num, realm->prior_parent_snaps,
            sizeof(u64)*realm->num_prior_parent_snaps);
     num += realm->num_prior_parent_snaps;
 
     sort(snapc->snaps, num, sizeof(u64), cmpu64_rev, NULL);
     snapc->num_snaps = num;
     dout("%s %llx %p: %p seq %lld (%u snaps)\n", __func__, realm->ino,
          realm, snapc, snapc->seq, (unsigned int) snapc->num_snaps);
 
     ceph_put_snap_context(realm->cached_context);
     realm->cached_context = snapc;
     /* queue realm for cap_snap creation */
     list_add_tail(&realm->dirty_item, dirty_realms);
     return 0;
 
 fail:
     /*
      * if we fail, clear old (incorrect) cached_context... hopefully
      * we'll have better luck building it later
      */
     if (realm->cached_context) {
         ceph_put_snap_context(realm->cached_context);
         realm->cached_context = NULL;
     }
     pr_err("%s %llx %p fail %d\n", __func__, realm->ino, realm, err);
     return err;
 }
 
 /*
  * rebuild snap context for the given realm and all of its children.
  */
 static void rebuild_snap_realms(struct ceph_snap_realm *realm,
                 struct list_head *dirty_realms)
 {
     LIST_HEAD(realm_queue);
     int last = 0;
     bool skip = false;
 
     list_add_tail(&realm->rebuild_item, &realm_queue);
 
     while (!list_empty(&realm_queue)) {
         struct ceph_snap_realm *_realm, *child;
 
         _realm = list_first_entry(&realm_queue,
                       struct ceph_snap_realm,
                       rebuild_item);
 
         /*
          * If the last building failed dues to memory
          * issue, just empty the realm_queue and return
          * to avoid infinite loop.
          */
         if (last < 0) {
             list_del_init(&_realm->rebuild_item);
             continue;
         }
 
         last = build_snap_context(_realm, &realm_queue, dirty_realms);
         dout("%s %llx %p, %s\n", __func__, _realm->ino, _realm,
              last > 0 ? "is deferred" : !last ? "succeeded" : "failed");
 
         /* is any child in the list ? */
         list_for_each_entry(child, &_realm->children, child_item) {
             if (!list_empty(&child->rebuild_item)) {
                 skip = true;
                 break;
             }
         }
 
         if (!skip) {
             list_for_each_entry(child, &_realm->children, child_item)
                 list_add_tail(&child->rebuild_item, &realm_queue);
         }
 
         /* last == 1 means need to build parent first */
         if (last <= 0)
             list_del_init(&_realm->rebuild_item);
     }
 }
 
 
 /*
  * helper to allocate and decode an array of snapids.  free prior
  * instance, if any.
  */
 static int dup_array(u64 **dst, __le64 *src, u32 num)
 {
     u32 i;
 
     kfree(*dst);
     if (num) {
         *dst = kcalloc(num, sizeof(u64), GFP_NOFS);
         if (!*dst)
             return -ENOMEM;
         for (i = 0; i < num; i++)
             (*dst)[i] = get_unaligned_le64(src + i);
     } else {
         *dst = NULL;
     }
     return 0;
 }
 
 static bool has_new_snaps(struct ceph_snap_context *o,
               struct ceph_snap_context *n)
 {
     if (n->num_snaps == 0)
         return false;
     /* snaps are in descending order */
     return n->snaps[0] > o->seq;
 }
 
 /*
  * When a snapshot is applied, the size/mtime inode metadata is queued
  * in a ceph_cap_snap (one for each snapshot) until writeback
  * completes and the metadata can be flushed back to the MDS.
  *
  * However, if a (sync) write is currently in-progress when we apply
  * the snapshot, we have to wait until the write succeeds or fails
  * (and a final size/mtime is known).  In this case the
  * cap_snap->writing = 1, and is said to be "pending."  When the write
  * finishes, we __ceph_finish_cap_snap().
  *
  * Caller must hold snap_rwsem for read (i.e., the realm topology won't
  * change).
  */
 static void ceph_queue_cap_snap(struct ceph_inode_info *ci,
                 struct ceph_cap_snap **pcapsnap)
 {
     struct inode *inode = &ci->netfs.inode;
     struct ceph_snap_context *old_snapc, *new_snapc;
     struct ceph_cap_snap *capsnap = *pcapsnap;
     struct ceph_buffer *old_blob = NULL;
     int used, dirty;
 
     spin_lock(&ci->i_ceph_lock);
     used = __ceph_caps_used(ci);
     dirty = __ceph_caps_dirty(ci);
 
     old_snapc = ci->i_head_snapc;
     new_snapc = ci->i_snap_realm->cached_context;
 
     /*
      * If there is a write in progress, treat that as a dirty Fw,
      * even though it hasn't completed yet; by the time we finish
      * up this capsnap it will be.
      */
     if (used & CEPH_CAP_FILE_WR)
         dirty |= CEPH_CAP_FILE_WR;
 
     if (__ceph_have_pending_cap_snap(ci)) {
         /* there is no point in queuing multiple "pending" cap_snaps,
            as no new writes are allowed to start when pending, so any
            writes in progress now were started before the previous
            cap_snap.  lucky us. */
         dout("%s %p %llx.%llx already pending\n",
              __func__, inode, ceph_vinop(inode));
         goto update_snapc;
     }
     if (ci->i_wrbuffer_ref_head == 0 &&
         !(dirty & (CEPH_CAP_ANY_EXCL|CEPH_CAP_FILE_WR))) {
         dout("%s %p %llx.%llx nothing dirty|writing\n",
              __func__, inode, ceph_vinop(inode));
         goto update_snapc;
     }
 
     BUG_ON(!old_snapc);
 
     /*
      * There is no need to send FLUSHSNAP message to MDS if there is
      * no new snapshot. But when there is dirty pages or on-going
      * writes, we still need to create cap_snap. cap_snap is needed
      * by the write path and page writeback path.
      *
      * also see ceph_try_drop_cap_snap()
      */
     if (has_new_snaps(old_snapc, new_snapc)) {
         if (dirty & (CEPH_CAP_ANY_EXCL|CEPH_CAP_FILE_WR))
             capsnap->need_flush = true;
     } else {
         if (!(used & CEPH_CAP_FILE_WR) &&
             ci->i_wrbuffer_ref_head == 0) {
             dout("%s %p %llx.%llx no new_snap|dirty_page|writing\n",
                  __func__, inode, ceph_vinop(inode));
             goto update_snapc;
         }
     }
 
     dout("%s %p %llx.%llx cap_snap %p queuing under %p %s %s\n",
          __func__, inode, ceph_vinop(inode), capsnap, old_snapc,
          ceph_cap_string(dirty), capsnap->need_flush ? "" : "no_flush");
     ihold(inode);
 
     capsnap->follows = old_snapc->seq;
     capsnap->issued = __ceph_caps_issued(ci, NULL);
     capsnap->dirty = dirty;
 
     capsnap->mode = inode->i_mode;
     capsnap->uid = inode->i_uid;
     capsnap->gid = inode->i_gid;
 
     if (dirty & CEPH_CAP_XATTR_EXCL) {
         old_blob = __ceph_build_xattrs_blob(ci);
         capsnap->xattr_blob =
             ceph_buffer_get(ci->i_xattrs.blob);
         capsnap->xattr_version = ci->i_xattrs.version;
     } else {
         capsnap->xattr_blob = NULL;
         capsnap->xattr_version = 0;
     }
 
     capsnap->inline_data = ci->i_inline_version != CEPH_INLINE_NONE;
 
     /* dirty page count moved from _head to this cap_snap;
        all subsequent writes page dirties occur _after_ this
        snapshot. */
     capsnap->dirty_pages = ci->i_wrbuffer_ref_head;
     ci->i_wrbuffer_ref_head = 0;
     capsnap->context = old_snapc;
     list_add_tail(&capsnap->ci_item, &ci->i_cap_snaps);
 
     if (used & CEPH_CAP_FILE_WR) {
         dout("%s %p %llx.%llx cap_snap %p snapc %p seq %llu used WR,"
              " now pending\n", __func__, inode, ceph_vinop(inode),
              capsnap, old_snapc, old_snapc->seq);
         capsnap->writing = 1;
     } else {
         /* note mtime, size NOW. */
         __ceph_finish_cap_snap(ci, capsnap);
     }
     *pcapsnap = NULL;
     old_snapc = NULL;
 
 update_snapc:
     if (ci->i_wrbuffer_ref_head == 0 &&
         ci->i_wr_ref == 0 &&
         ci->i_dirty_caps == 0 &&
         ci->i_flushing_caps == 0) {
         ci->i_head_snapc = NULL;
     } else {
         ci->i_head_snapc = ceph_get_snap_context(new_snapc);
         dout(" new snapc is %p\n", new_snapc);
     }
     spin_unlock(&ci->i_ceph_lock);
 
     ceph_buffer_put(old_blob);
     ceph_put_snap_context(old_snapc);
 }
 
 /*
  * Finalize the size, mtime for a cap_snap.. that is, settle on final values
  * to be used for the snapshot, to be flushed back to the mds.
  *
  * If capsnap can now be flushed, add to snap_flush list, and return 1.
  *
  * Caller must hold i_ceph_lock.
  */
 int __ceph_finish_cap_snap(struct ceph_inode_info *ci,
                 struct ceph_cap_snap *capsnap)
 {
     struct inode *inode = &ci->netfs.inode;
     struct ceph_mds_client *mdsc = ceph_sb_to_mdsc(inode->i_sb);
 
     BUG_ON(capsnap->writing);
     capsnap->size = i_size_read(inode);
     capsnap->mtime = inode->i_mtime;
     capsnap->atime = inode->i_atime;
     capsnap->ctime = inode->i_ctime;
     capsnap->btime = ci->i_btime;
     capsnap->change_attr = inode_peek_iversion_raw(inode);
     capsnap->time_warp_seq = ci->i_time_warp_seq;
     capsnap->truncate_size = ci->i_truncate_size;
     capsnap->truncate_seq = ci->i_truncate_seq;
     if (capsnap->dirty_pages) {
         dout("%s %p %llx.%llx cap_snap %p snapc %p %llu %s s=%llu "
              "still has %d dirty pages\n", __func__, inode,
              ceph_vinop(inode), capsnap, capsnap->context,
              capsnap->context->seq, ceph_cap_string(capsnap->dirty),
              capsnap->size, capsnap->dirty_pages);
         return 0;
     }
 
     /* Fb cap still in use, delay it */
     if (ci->i_wb_ref) {
         dout("%s %p %llx.%llx cap_snap %p snapc %p %llu %s s=%llu "
              "used WRBUFFER, delaying\n", __func__, inode,
              ceph_vinop(inode), capsnap, capsnap->context,
              capsnap->context->seq, ceph_cap_string(capsnap->dirty),
              capsnap->size);
         capsnap->writing = 1;
         return 0;
     }
 
     ci->i_ceph_flags |= CEPH_I_FLUSH_SNAPS;
     dout("%s %p %llx.%llx cap_snap %p snapc %p %llu %s s=%llu\n",
          __func__, inode, ceph_vinop(inode), capsnap, capsnap->context,
          capsnap->context->seq, ceph_cap_string(capsnap->dirty),
          capsnap->size);
 
     spin_lock(&mdsc->snap_flush_lock);
     if (list_empty(&ci->i_snap_flush_item))
         list_add_tail(&ci->i_snap_flush_item, &mdsc->snap_flush_list);
     spin_unlock(&mdsc->snap_flush_lock);
     return 1;  /* caller may want to ceph_flush_snaps */
 }
 
 /*
  * Queue cap_snaps for snap writeback for this realm and its children.
  * Called under snap_rwsem, so realm topology won't change.
  */
 static void queue_realm_cap_snaps(struct ceph_snap_realm *realm)
 {
     struct ceph_inode_info *ci;
     struct inode *lastinode = NULL;
     struct ceph_cap_snap *capsnap = NULL;
 
     dout("%s %p %llx inode\n", __func__, realm, realm->ino);
 
     spin_lock(&realm->inodes_with_caps_lock);
     list_for_each_entry(ci, &realm->inodes_with_caps, i_snap_realm_item) {
         struct inode *inode = igrab(&ci->netfs.inode);
         if (!inode)
             continue;
         spin_unlock(&realm->inodes_with_caps_lock);
         iput(lastinode);
         lastinode = inode;
 
         /*
          * Allocate the capsnap memory outside of ceph_queue_cap_snap()
          * to reduce very possible but unnecessary frequently memory
          * allocate/free in this loop.
          */
         if (!capsnap) {
             capsnap = kmem_cache_zalloc(ceph_cap_snap_cachep, GFP_NOFS);
             if (!capsnap) {
                 pr_err("ENOMEM allocating ceph_cap_snap on %p\n",
                        inode);
                 return;
             }
         }
         capsnap->cap_flush.is_capsnap = true;
         refcount_set(&capsnap->nref, 1);
         INIT_LIST_HEAD(&capsnap->cap_flush.i_list);
         INIT_LIST_HEAD(&capsnap->cap_flush.g_list);
         INIT_LIST_HEAD(&capsnap->ci_item);
 
         ceph_queue_cap_snap(ci, &capsnap);
         spin_lock(&realm->inodes_with_caps_lock);
     }
     spin_unlock(&realm->inodes_with_caps_lock);
     iput(lastinode);
 
     if (capsnap)
         kmem_cache_free(ceph_cap_snap_cachep, capsnap);
     dout("%s %p %llx done\n", __func__, realm, realm->ino);
 }
 
 /*
  * Parse and apply a snapblob "snap trace" from the MDS.  This specifies
  * the snap realm parameters from a given realm and all of its ancestors,
  * up to the root.
  *
  * Caller must hold snap_rwsem for write.
  */
 int ceph_update_snap_trace(struct ceph_mds_client *mdsc,
                void *p, void *e, bool deletion,
                struct ceph_snap_realm **realm_ret)
 {
     struct ceph_mds_snap_realm *ri;    /* encoded */
     __le64 *snaps;                     /* encoded */
     __le64 *prior_parent_snaps;        /* encoded */
     struct ceph_snap_realm *realm = NULL;
     struct ceph_snap_realm *first_realm = NULL;
     struct ceph_snap_realm *realm_to_rebuild = NULL;
     int rebuild_snapcs;
     int err = -ENOMEM;
     LIST_HEAD(dirty_realms);
 
     lockdep_assert_held_write(&mdsc->snap_rwsem);
 
     dout("%s deletion=%d\n", __func__, deletion);
 more:
     rebuild_snapcs = 0;
     ceph_decode_need(&p, e, sizeof(*ri), bad);
     ri = p;
     p += sizeof(*ri);
     ceph_decode_need(&p, e, sizeof(u64)*(le32_to_cpu(ri->num_snaps) +
                 le32_to_cpu(ri->num_prior_parent_snaps)), bad);
     snaps = p;
     p += sizeof(u64) * le32_to_cpu(ri->num_snaps);
     prior_parent_snaps = p;
     p += sizeof(u64) * le32_to_cpu(ri->num_prior_parent_snaps);
 
     realm = ceph_lookup_snap_realm(mdsc, le64_to_cpu(ri->ino));
     if (!realm) {
         realm = ceph_create_snap_realm(mdsc, le64_to_cpu(ri->ino));
         if (IS_ERR(realm)) {
             err = PTR_ERR(realm);
             goto fail;
         }
     }
 
     /* ensure the parent is correct */
     err = adjust_snap_realm_parent(mdsc, realm, le64_to_cpu(ri->parent));
     if (err < 0)
         goto fail;
     rebuild_snapcs += err;
 
     if (le64_to_cpu(ri->seq) > realm->seq) {
         dout("%s updating %llx %p %lld -> %lld\n", __func__,
              realm->ino, realm, realm->seq, le64_to_cpu(ri->seq));
         /* update realm parameters, snap lists */
         realm->seq = le64_to_cpu(ri->seq);
         realm->created = le64_to_cpu(ri->created);
         realm->parent_since = le64_to_cpu(ri->parent_since);
 
         realm->num_snaps = le32_to_cpu(ri->num_snaps);
         err = dup_array(&realm->snaps, snaps, realm->num_snaps);
         if (err < 0)
             goto fail;
 
         realm->num_prior_parent_snaps =
             le32_to_cpu(ri->num_prior_parent_snaps);
         err = dup_array(&realm->prior_parent_snaps, prior_parent_snaps,
                 realm->num_prior_parent_snaps);
         if (err < 0)
             goto fail;
 
         if (realm->seq > mdsc->last_snap_seq)
             mdsc->last_snap_seq = realm->seq;
 
         rebuild_snapcs = 1;
     } else if (!realm->cached_context) {
         dout("%s %llx %p seq %lld new\n", __func__,
              realm->ino, realm, realm->seq);
         rebuild_snapcs = 1;
     } else {
         dout("%s %llx %p seq %lld unchanged\n", __func__,
              realm->ino, realm, realm->seq);
     }
 
     dout("done with %llx %p, rebuild_snapcs=%d, %p %p\n", realm->ino,
          realm, rebuild_snapcs, p, e);
 
     /*
      * this will always track the uppest parent realm from which
      * we need to rebuild the snapshot contexts _downward_ in
      * hierarchy.
      */
     if (rebuild_snapcs)
         realm_to_rebuild = realm;
 
     /* rebuild_snapcs when we reach the _end_ (root) of the trace */
     if (realm_to_rebuild && p >= e)
         rebuild_snap_realms(realm_to_rebuild, &dirty_realms);
 
     if (!first_realm)
         first_realm = realm;
     else
         ceph_put_snap_realm(mdsc, realm);
 
     if (p < e)
         goto more;
 
     /*
      * queue cap snaps _after_ we've built the new snap contexts,
      * so that i_head_snapc can be set appropriately.
      */
     while (!list_empty(&dirty_realms)) {
         realm = list_first_entry(&dirty_realms, struct ceph_snap_realm,
                      dirty_item);
         list_del_init(&realm->dirty_item);
         queue_realm_cap_snaps(realm);
     }
 
     if (realm_ret)
         *realm_ret = first_realm;
     else
         ceph_put_snap_realm(mdsc, first_realm);
 
     __cleanup_empty_realms(mdsc);
     return 0;
 
 bad:
     err = -EIO;
 fail:
     if (realm && !IS_ERR(realm))
         ceph_put_snap_realm(mdsc, realm);
     if (first_realm)
         ceph_put_snap_realm(mdsc, first_realm);
     pr_err("%s error %d\n", __func__, err);
     return err;
 }
 
 
 /*
  * Send any cap_snaps that are queued for flush.  Try to carry
  * s_mutex across multiple snap flushes to avoid locking overhead.
  *
  * Caller holds no locks.
  */
 static void flush_snaps(struct ceph_mds_client *mdsc)
 {
     struct ceph_inode_info *ci;
     struct inode *inode;
     struct ceph_mds_session *session = NULL;
 
     dout("%s\n", __func__);
     spin_lock(&mdsc->snap_flush_lock);
     while (!list_empty(&mdsc->snap_flush_list)) {
         ci = list_first_entry(&mdsc->snap_flush_list,
                 struct ceph_inode_info, i_snap_flush_item);
         inode = &ci->netfs.inode;
         ihold(inode);
         spin_unlock(&mdsc->snap_flush_lock);
         ceph_flush_snaps(ci, &session);
         iput(inode);
         spin_lock(&mdsc->snap_flush_lock);
     }
     spin_unlock(&mdsc->snap_flush_lock);
 
     ceph_put_mds_session(session);
     dout("%s done\n", __func__);
 }
 
 /**
  * ceph_change_snap_realm - change the snap_realm for an inode
  * @inode: inode to move to new snap realm
  * @realm: new realm to move inode into (may be NULL)
  *
  * Detach an inode from its old snaprealm (if any) and attach it to
  * the new snaprealm (if any). The old snap realm reference held by
  * the inode is put. If realm is non-NULL, then the caller's reference
  * to it is taken over by the inode.
  */
 void ceph_change_snap_realm(struct inode *inode, struct ceph_snap_realm *realm)
 {
     struct ceph_inode_info *ci = ceph_inode(inode);
     struct ceph_mds_client *mdsc = ceph_inode_to_client(inode)->mdsc;
     struct ceph_snap_realm *oldrealm = ci->i_snap_realm;
 
     lockdep_assert_held(&ci->i_ceph_lock);
 
     if (oldrealm) {
         spin_lock(&oldrealm->inodes_with_caps_lock);
         list_del_init(&ci->i_snap_realm_item);
         if (oldrealm->ino == ci->i_vino.ino)
             oldrealm->inode = NULL;
         spin_unlock(&oldrealm->inodes_with_caps_lock);
         ceph_put_snap_realm(mdsc, oldrealm);
     }
 
     ci->i_snap_realm = realm;
 
     if (realm) {
         spin_lock(&realm->inodes_with_caps_lock);
         list_add(&ci->i_snap_realm_item, &realm->inodes_with_caps);
         if (realm->ino == ci->i_vino.ino)
             realm->inode = inode;
         spin_unlock(&realm->inodes_with_caps_lock);
     }
 }
 
 /*
  * Handle a snap notification from the MDS.
  *
  * This can take two basic forms: the simplest is just a snap creation
  * or deletion notification on an existing realm.  This should update the
  * realm and its children.
  *
  * The more difficult case is realm creation, due to snap creation at a
  * new point in the file hierarchy, or due to a rename that moves a file or
  * directory into another realm.
  */
 void ceph_handle_snap(struct ceph_mds_client *mdsc,
               struct ceph_mds_session *session,
               struct ceph_msg *msg)
 {
     struct super_block *sb = mdsc->fsc->sb;
     int mds = session->s_mds;
     u64 split;
     int op;
     int trace_len;
     struct ceph_snap_realm *realm = NULL;
     void *p = msg->front.iov_base;
     void *e = p + msg->front.iov_len;
     struct ceph_mds_snap_head *h;
     int num_split_inos, num_split_realms;
     __le64 *split_inos = NULL, *split_realms = NULL;
     int i;
     int locked_rwsem = 0;
 
     /* decode */
     if (msg->front.iov_len < sizeof(*h))
         goto bad;
     h = p;
     op = le32_to_cpu(h->op);
     split = le64_to_cpu(h->split);   /* non-zero if we are splitting an
                       * existing realm */
     num_split_inos = le32_to_cpu(h->num_split_inos);
     num_split_realms = le32_to_cpu(h->num_split_realms);
     trace_len = le32_to_cpu(h->trace_len);
     p += sizeof(*h);
 
     dout("%s from mds%d op %s split %llx tracelen %d\n", __func__,
          mds, ceph_snap_op_name(op), split, trace_len);
 
     mutex_lock(&session->s_mutex);
     inc_session_sequence(session);
     mutex_unlock(&session->s_mutex);
 
     down_write(&mdsc->snap_rwsem);
     locked_rwsem = 1;
 
     if (op == CEPH_SNAP_OP_SPLIT) {
         struct ceph_mds_snap_realm *ri;
 
         /*
          * A "split" breaks part of an existing realm off into
          * a new realm.  The MDS provides a list of inodes
          * (with caps) and child realms that belong to the new
          * child.
          */
         split_inos = p;
         p += sizeof(u64) * num_split_inos;
         split_realms = p;
         p += sizeof(u64) * num_split_realms;
         ceph_decode_need(&p, e, sizeof(*ri), bad);
         /* we will peek at realm info here, but will _not_
          * advance p, as the realm update will occur below in
          * ceph_update_snap_trace. */
         ri = p;
 
         realm = ceph_lookup_snap_realm(mdsc, split);
         if (!realm) {
             realm = ceph_create_snap_realm(mdsc, split);
             if (IS_ERR(realm))
                 goto out;
         }
 
         dout("splitting snap_realm %llx %p\n", realm->ino, realm);
         for (i = 0; i < num_split_inos; i++) {
             struct ceph_vino vino = {
                 .ino = le64_to_cpu(split_inos[i]),
                 .snap = CEPH_NOSNAP,
             };
             struct inode *inode = ceph_find_inode(sb, vino);
             struct ceph_inode_info *ci;
 
             if (!inode)
                 continue;
             ci = ceph_inode(inode);
 
             spin_lock(&ci->i_ceph_lock);
             if (!ci->i_snap_realm)
                 goto skip_inode;
             /*
              * If this inode belongs to a realm that was
              * created after our new realm, we experienced
              * a race (due to another split notifications
              * arriving from a different MDS).  So skip
              * this inode.
              */
             if (ci->i_snap_realm->created >
                 le64_to_cpu(ri->created)) {
                 dout(" leaving %p %llx.%llx in newer realm %llx %p\n",
                      inode, ceph_vinop(inode), ci->i_snap_realm->ino,
                      ci->i_snap_realm);
                 goto skip_inode;
             }
             dout(" will move %p %llx.%llx to split realm %llx %p\n",
                  inode, ceph_vinop(inode), realm->ino, realm);
 
             ceph_get_snap_realm(mdsc, realm);
             ceph_change_snap_realm(inode, realm);
             spin_unlock(&ci->i_ceph_lock);
             iput(inode);
             continue;
 
 skip_inode:
             spin_unlock(&ci->i_ceph_lock);
             iput(inode);
         }
 
         /* we may have taken some of the old realm's children. */
         for (i = 0; i < num_split_realms; i++) {
             struct ceph_snap_realm *child =
                 __lookup_snap_realm(mdsc,
                        le64_to_cpu(split_realms[i]));
             if (!child)
                 continue;
             adjust_snap_realm_parent(mdsc, child, realm->ino);
         }
     }
 
     /*
      * update using the provided snap trace. if we are deleting a
      * snap, we can avoid queueing cap_snaps.
      */
     ceph_update_snap_trace(mdsc, p, e,
                    op == CEPH_SNAP_OP_DESTROY, NULL);
 
     if (op == CEPH_SNAP_OP_SPLIT)
         /* we took a reference when we created the realm, above */
         ceph_put_snap_realm(mdsc, realm);
 
     __cleanup_empty_realms(mdsc);
 
     up_write(&mdsc->snap_rwsem);
 
     flush_snaps(mdsc);
     return;
 
 bad:
     pr_err("%s corrupt snap message from mds%d\n", __func__, mds);
     ceph_msg_dump(msg);
 out:
     if (locked_rwsem)
         up_write(&mdsc->snap_rwsem);
     return;
 }
 
 struct ceph_snapid_map* ceph_get_snapid_map(struct ceph_mds_client *mdsc,
                         u64 snap)
 {
     struct ceph_snapid_map *sm, *exist;
     struct rb_node **p, *parent;
     int ret;
 
     exist = NULL;
     spin_lock(&mdsc->snapid_map_lock);
     p = &mdsc->snapid_map_tree.rb_node;
     while (*p) {
         exist = rb_entry(*p, struct ceph_snapid_map, node);
         if (snap > exist->snap) {
             p = &(*p)->rb_left;
         } else if (snap < exist->snap) {
             p = &(*p)->rb_right;
         } else {
             if (atomic_inc_return(&exist->ref) == 1)
                 list_del_init(&exist->lru);
             break;
         }
         exist = NULL;
     }
     spin_unlock(&mdsc->snapid_map_lock);
     if (exist) {
         dout("%s found snapid map %llx -> %x\n", __func__,
              exist->snap, exist->dev);
         return exist;
     }
 
     sm = kmalloc(sizeof(*sm), GFP_NOFS);
     if (!sm)
         return NULL;
 
     ret = get_anon_bdev(&sm->dev);
     if (ret < 0) {
         kfree(sm);
         return NULL;
     }
 
     INIT_LIST_HEAD(&sm->lru);
     atomic_set(&sm->ref, 1);
     sm->snap = snap;
 
     exist = NULL;
     parent = NULL;
     p = &mdsc->snapid_map_tree.rb_node;
     spin_lock(&mdsc->snapid_map_lock);
     while (*p) {
         parent = *p;
         exist = rb_entry(*p, struct ceph_snapid_map, node);
         if (snap > exist->snap)
             p = &(*p)->rb_left;
         else if (snap < exist->snap)
             p = &(*p)->rb_right;
         else
             break;
         exist = NULL;
     }
     if (exist) {
         if (atomic_inc_return(&exist->ref) == 1)
             list_del_init(&exist->lru);
     } else {
         rb_link_node(&sm->node, parent, p);
         rb_insert_color(&sm->node, &mdsc->snapid_map_tree);
     }
     spin_unlock(&mdsc->snapid_map_lock);
     if (exist) {
         free_anon_bdev(sm->dev);
         kfree(sm);
         dout("%s found snapid map %llx -> %x\n", __func__,
              exist->snap, exist->dev);
         return exist;
     }
 
     dout("%s create snapid map %llx -> %x\n", __func__,
          sm->snap, sm->dev);
     return sm;
 }
 
 void ceph_put_snapid_map(struct ceph_mds_client* mdsc,
              struct ceph_snapid_map *sm)
 {
     if (!sm)
         return;
     if (atomic_dec_and_lock(&sm->ref, &mdsc->snapid_map_lock)) {
         if (!RB_EMPTY_NODE(&sm->node)) {
             sm->last_used = jiffies;
             list_add_tail(&sm->lru, &mdsc->snapid_map_lru);
             spin_unlock(&mdsc->snapid_map_lock);
         } else {
             /* already cleaned up by
              * ceph_cleanup_snapid_map() */
             spin_unlock(&mdsc->snapid_map_lock);
             kfree(sm);
         }
     }
 }
 
 void ceph_trim_snapid_map(struct ceph_mds_client *mdsc)
 {
     struct ceph_snapid_map *sm;
     unsigned long now;
     LIST_HEAD(to_free);
 
     spin_lock(&mdsc->snapid_map_lock);
     now = jiffies;
 
     while (!list_empty(&mdsc->snapid_map_lru)) {
         sm = list_first_entry(&mdsc->snapid_map_lru,
                       struct ceph_snapid_map, lru);
         if (time_after(sm->last_used + CEPH_SNAPID_MAP_TIMEOUT, now))
             break;
 
         rb_erase(&sm->node, &mdsc->snapid_map_tree);
         list_move(&sm->lru, &to_free);
     }
     spin_unlock(&mdsc->snapid_map_lock);
 
     while (!list_empty(&to_free)) {
         sm = list_first_entry(&to_free, struct ceph_snapid_map, lru);
         list_del(&sm->lru);
         dout("trim snapid map %llx -> %x\n", sm->snap, sm->dev);
         free_anon_bdev(sm->dev);
         kfree(sm);
     }
 }
 
 void ceph_cleanup_snapid_map(struct ceph_mds_client *mdsc)
 {
     struct ceph_snapid_map *sm;
     struct rb_node *p;
     LIST_HEAD(to_free);
 
     spin_lock(&mdsc->snapid_map_lock);
     while ((p = rb_first(&mdsc->snapid_map_tree))) {
         sm = rb_entry(p, struct ceph_snapid_map, node);
         rb_erase(p, &mdsc->snapid_map_tree);
         RB_CLEAR_NODE(p);
         list_move(&sm->lru, &to_free);
     }
     spin_unlock(&mdsc->snapid_map_lock);
 
     while (!list_empty(&to_free)) {
         sm = list_first_entry(&to_free, struct ceph_snapid_map, lru);
         list_del(&sm->lru);
         free_anon_bdev(sm->dev);
         if (WARN_ON_ONCE(atomic_read(&sm->ref))) {
             pr_err("snapid map %llx -> %x still in use\n",
                    sm->snap, sm->dev);
         }
         kfree(sm);
     }
 }

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